is only desirable to modify the design when the data for some defined form is fully established and available as a standard of reference.
In experimenting with mica models the author has frequently adopted the form of natural flexion of an elliptical mica plate secured to a central bolster, to give the desired mid-section form; the grading is found to take the form given approximately in Fig. 121. In other cases the mica plate has been artificially graded to approximate to the standard given above, by fitting additional ribs as shown in Fig. 122.
Fig. 123.
§ 193. On the Measurement of "Sail Area."—The appropriate measurement of the sail area or wing area of birds of various species is a rather vexed question. Some writers have regarded the wings as the sole organs of support, and the actual wing area alone has been reckoned as effective. Others (notably M. Moulliard) have assumed that the whole plan area (or ombre) of the bird contributes to the support, and have made pressure computations on this basis.
The author's view is that the influence of the body as a supporting member cannot be ignored, but that probably its effect can be best estimated as equivalent to an imaginary band of appropriate width forming a junction between the two extended wings as represented in Fig. 123. This view is based on the knowledge that the cyclic system must be continuous from wing to wing, and, on the whole, will produce a reaction on the body
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